Rock soapwort

Questions about rock soapwort

Does rock soapwort need sun or shade?

Rock soapwort grows in full sun (6 or more hours of direct sun a day).

It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled. Once settled in, it stands drought.

What zones does rock soapwort grow in?

USDA zones 3 to 8. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).

Above zone 8 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does rock soapwort flower in my zone?

In zone 5 it flowers mid May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should rock soapwort be planted?

18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is about its full width, so each plant keeps its own outline.

It grows 8 in (20 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many rock soapwort plants do I need?

At 18 in apart, set out in staggered rows:

• 5 to fill 10 square feet (about 1 m²)
• 7 for a single row 10 ft (3 m) long
• 17 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as threes and fives, along the front and just behind it.

In the bed above, the planner used five in one group.

Is rock soapwort poisonous to dogs and cats?

No toxicity is recorded for dogs, cats, horses or people, according to NC State Extension.

"Not toxic" is not "edible": a pet that eats a lot of any plant can be sick.

Is there a native plant like rock soapwort?

Rock soapwort comes from Spain, South West and South Central Europe. These North American natives come closest to doing its job:

• Woolly yarrow: the same job in a bed and the same flowering time; 6 in narrower, yellow, not pink.
• Rock cress: the same job in a bed and the same colour; 6 in narrower, flowers mid April to early May.
• Creeping phlox: the same job in a bed, the same size and the same colour; flowers mid April to mid May, wants average soil.

Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.

Do deer eat rock soapwort?

Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

Will rock soapwort spread?

It seeds itself about; the risk of it taking over is moderate. Self-seeds freely. Remove the spent flowers to limit seedlings.

What flowers after rock soapwort?

Rock soapwort is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:

• Black-eyed Susan: from mid July to mid September, 24 in tall.
• Butterfly weed: from late June to early August, 24 in tall.
• Carpathian bellflower 'Blue Clips': from late June to late August, 8 in tall.

What does rock soapwort look like in winter?

Rock soapwort holds some of its leaves into winter, more in a mild year or a sheltered spot, and they look tired by March. Cut the old ones off as new growth starts.